1. Field of the Invention
The invention relates to a method of sorting mailpieces in at least two sorting passes in a sorting machine with sorting outlets into which the mailpieces are directed from an unstacking inlet, wherein, in the first sorting pass, images are formed of the surfaces of the mailpieces so as to derive first image signatures serving as unique identifiers for the mailpieces in the machine, wherein, in the second sorting pass for sorting the mailpieces, an image of the surface of a current mailpiece is formed again so as to derive a current image signature associated with the current mailpiece, and first image signatures grouped together in a set in an exploration memory space are scanned in order to detect a match with said current signature, and wherein the mailpieces are transferred manually using storage trays from the sorting outlets to the unstacking inlet between the two sorting passes.
2. Discussion of the Background Art
The process for generating such image signatures or digital “fingerprints” for the mailpieces and how to compare two image signatures for detecting a match is described in Patent Document EP 1 519 796. FIG. 1 shows a face of a mailpiece M that bears a delivery address A. The image signature serving as a unique identifier for the mailpiece in accordance with the method of the invention is derived from the image of the surface of the mailpiece that bears the delivery address A and said image signature typically comprises an image component representative of the graphical characteristics of the image (e.g. histograms of the shades of gray in various distinct portions of a plurality of grids applied over the image) and a postal component representative of the characteristics of the delivery address A (number of signs in the address, position of the address block in the image, etc). In principle, these two components should not be correlated to each other in order to guarantee that the identifier is totally unique.
FIG. 2 is a highly diagrammatic view of a sorting machine 1 having an inlet unstacker 2 for inserting mailpieces into the machine, a device 3 for forming images of the surfaces of the mailpieces, and a conveyor 4 that directs the mailpieces in series towards the sorting outlets 7. The sorting machine 1 is monitored and controlled by a data processing unit 5 having a memory DB. The unit 5 can be connected in a manner known per se to video coding units 6.
A storage tray 8 is also shown, by means of which an operator transfers the mailpieces from the sorting outlets to the inlet of the machine between two sorting passes (arrow between the outlets 7 and the tray 8, and arrow between the tray 8 and the unstacker 2). It should be understood that a plurality of trays such as 8 are used to transfer the mailpieces between all of the outlets 7 and the inlet 2 of the machine. Reference 9 in FIG. 2 designates a set of labeling machines that act on command to deliver coded labels 10 to be affixed to the trays such as 8. A scanner (not shown) is provided at the inlet of the machine so as to read back the labels on the trays and so as to have them identified by the unit 5.
Conventionally, during a first sorting pass, mailpieces such as M are thus inserted manually by the operator into the inlet unstacker 2 of the sorting machine 1. The mailpieces are unstacked so as to be put in series and conveyed on edge past the device 3 so as to form a digital image of the surface of each mailpiece. An image signature is derived from the image of the surface of each mailpiece by the unit 5 and is put into correspondence in the memory DB with sorting data read from the image by Optical Character Recognition (OCR) and/or by video-coding.
The mailpieces directed into the sorting outlets are then transferred using trays 8 to the inlet of the sorting machine for a new sorting pass. Where appropriate, the second sorting pass could be performed on another sorting machine.
For the second sorting pass, the mailpieces are emptied manually from the storage trays 8 by the operator and they are placed in the magazine of the inlet unstacker 2 so that, once again, they are put into series and are conveyed past the device 3 where an image of the surface of each current mailpiece bearing the address A is formed again, and a current image signature is computed again for each current mailpiece by the unit 5. On the basis of a current signature, the unit 5 scans, in the memory, the signatures computed during the first sorting pass, so as to detect a match between one of said signatures and the current signature, with a view to retrieving sorting data from the memory DB.
Document EP 1 222 037 describes a method of limiting the amount of signature exploration space that is to be scanned in a memory, that method relying on strict compliance with the chronological order for the mailpieces in the trays and then in the magazine of the inlet unstacker.
However, with sorting outlets of the accumulation type in which the mailpieces are stacked by means of a stacker, chronological order need not necessarily be preserved, e.g. if the mailpieces are mishandled while they are being stored in or emptied from a tray.
That known method of optimizing the size of memory space for image signature exploration is therefore not suitable for a sorting machine with accumulation sorting outlets, i.e. with outlets having stackers. Unfortunately, that type of sorting outlet is in wide use for sorting mail of C5 format in compliance with Standard ISO-269.